realtime_publisher.h

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/*
 * Copyright (c) 2008, Willow Garage, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the Willow Garage, Inc. nor the names of its
 *       contributors may be used to endorse or promote products derived from
 *       this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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 */

/*
 * Publishing ROS messages is difficult, as the publish function is
 * not realtime safe.  This class provides the proper locking so that
 * you can call publish in realtime and a separate (non-realtime)
 * thread will ensure that the message gets published over ROS.
 *
 * Author: Stuart Glaser
 */
#ifndef REALTIME_TOOLS__REALTIME_PUBLISHER_H_
#define REALTIME_TOOLS__REALTIME_PUBLISHER_H_

#include <string>
#include <ros/node_handle.h>
#include <chrono>
#include <condition_variable>
#include <memory>
#include <mutex>
#include <thread>

namespace realtime_tools {

template <class Msg>
class RealtimePublisher
{

public:
  Msg msg_;
  
  RealtimePublisher(const ros::NodeHandle &node, const std::string &topic, int queue_size, bool latched=false)
    : topic_(topic), node_(node), is_running_(false), keep_running_(false), turn_(LOOP_NOT_STARTED)
  {
    construct(queue_size, latched);
  }

  RealtimePublisher()
    : is_running_(false), keep_running_(false), turn_(LOOP_NOT_STARTED)
  {
  }

  ~RealtimePublisher()
  {
    stop();
    while (is_running())
    {
      std::this_thread::sleep_for(std::chrono::microseconds(100));
    }

    if (thread_.joinable())
    {
      thread_.join();
    }
    publisher_.shutdown();
  }

  void init(const ros::NodeHandle &node, const std::string &topic, int queue_size, bool latched=false)
  {
    topic_ = topic;
    node_ = node;
    construct(queue_size, latched);
  }

  void stop()
  {
    keep_running_ = false;
#ifdef NON_POLLING
    updated_cond_.notify_one();  // So the publishing loop can exit
#endif
  }

  bool trylock()
  {
    if (msg_mutex_.try_lock())
    {
      if (turn_ == REALTIME)
      {
        return true;
      }
      else
      {
        msg_mutex_.unlock();
        return false;
      }
    }
    else
    {
      return false;
    }
  }

  void unlockAndPublish()
  {
    turn_ = NON_REALTIME;
    msg_mutex_.unlock();
#ifdef NON_POLLING
    updated_cond_.notify_one();
#endif
  }

  void lock()
  {
#ifdef NON_POLLING
    msg_mutex_.lock();
#else
    // never actually block on the lock
    while (!msg_mutex_.try_lock())
    {
      std::this_thread::sleep_for(std::chrono::microseconds(200));
    }
#endif
  }

  void unlock()
  {
    msg_mutex_.unlock();
  }

private:
  // non-copyable
  RealtimePublisher(const RealtimePublisher &) = delete;
  RealtimePublisher & operator=(const RealtimePublisher &) = delete;

  void construct(int queue_size, bool latched=false)
  {
    publisher_ = node_.advertise<Msg>(topic_, queue_size, latched);
    keep_running_ = true;
    thread_ = std::thread(&RealtimePublisher::publishingLoop, this);
  }


  bool is_running() const { return is_running_; }

  void publishingLoop()
  {
    is_running_ = true;
    turn_ = REALTIME;

    while (keep_running_)
    {
      Msg outgoing;

      // Locks msg_ and copies it
      lock();
      while (turn_ != NON_REALTIME && keep_running_)
      {
#ifdef NON_POLLING
        updated_cond_.wait(lock);
#else
        unlock();
        std::this_thread::sleep_for(std::chrono::microseconds(500));
        lock();
#endif
      }
      outgoing = msg_;
      turn_ = REALTIME;

      unlock();

      // Sends the outgoing message
      if (keep_running_)
        publisher_.publish(outgoing);
    }
    is_running_ = false;
  }

  std::string topic_;
  ros::NodeHandle node_;
  ros::Publisher publisher_;
  volatile bool is_running_;
  volatile bool keep_running_;

  std::thread thread_;

  std::mutex msg_mutex_;  // Protects msg_

#ifdef NON_POLLING
  std::condition_variable updated_cond_;
#endif

  enum {REALTIME, NON_REALTIME, LOOP_NOT_STARTED};
  int turn_;  // Who's turn is it to use msg_?
};

template <class Msg>
using RealtimePublisherSharedPtr = std::shared_ptr<RealtimePublisher<Msg> >;

}

#endif